The present invention relates to the field of semiconductor device fabrication, and more particularly to methods for making conductive contacts in the formation of a semiconductor device.
As semiconductor fabrication moves toward maximizing circuit density, electrical components are formed at a number of layers and different locations. This requires electrical connection between metal layers or other conductive layers at different elevations in the substrate. Such interconnections are typically provided by forming a contact opening through insulating layer to the underlying conductive feature. With increasing circuit density, the dimensions of openings for electrical contacts become narrower and deeper, posing a challenge to provide adequate conductive fill within high aspect ratio openings.
Typically, in forming a contact plug, a thin layer of titanium is deposited over the top of a silicon base layer (substrate), and tungsten or other electrically conductive plug material is then deposited from tungsten hexafluoride (WF6) by chemical vapor deposition (CVD) to fill the contact hole. However, there are several limitations of tungsten (W) plugs. Tungsten does not provide an adequate fill for high aspect ratio features. In addition, the use of WF6 as a precursor gas in the formation of tungsten plugs, can result in the penetration of the fluoride component into the adjacent dielectric layer causing lateral encroachment and wormholes.
Titanium nitride (TiN) films have attractive properties that may overcome the limitations of tungsten plugs as integrated circuit (IC) devices continue to shrink below 0.15 micron dimension. TiN films have been deposited by low pressure chemical vapor deposition (LPCVD) using tetrakisdimethyl-amidotitanium (TDMAT) and ammonia as precursor gases. However, TDMAT films have a high carbon content and when subjected to high temperatures in the presence of oxygen, become porous and, therefore, are unusable as a conductive contact.
Thin TiN films and liners have also been deposited from titanium tetrachloride (TiCl4) and ammonia (NH3) by CVD onto a titanium (Ti) liner overlying the insulative layer. Although useful for forming a thin liner, when pure TiCl4-based TiN is deposited to fill a via or other contact opening, the material does not adhere well to the Ti thin layer, particularly when the TiN layer becomes greater than about 150 to about 200 angstroms thick.
Therefore, it would be desirable to provide a titanium nitride material that can be used as a replacement fill material for tungsten in forming conductive contacts in high aspect ratio features in a semiconductor device.
The present invention provides methods for forming conductive contacts in the construction of semiconductive devices, and the conductive components formed by those methods. The method is useful for fabricating contacts to electrical components beneath an insulation layer in an integrated circuit such as memory devices.
The present TiCl4-based titanium nitride films are particularly useful as conductive contacts to replace tungsten (W) plugs in high aspect ratio features, particularly openings and other features having an aspect ratio of 3:1 or greater. The films also overcome inadequacies of pure TiCl4-based titanium nitride films that are used as fill material for forming conductive contacts or interconnects within contact openings formed through an insulative layer of a semiconductor structure. Pure TiCl4-based titanium nitride fills do not adhere well to the surface of insulative sidewalls of a contact opening, and can also cause the insulative layer to crack due, at least in part, to the pressure exerted when the thickness of the fill within the contact opening is about 200 angstroms or greater.
The present invention overcomes the problems of a pure TiCl4-based titanium nitride plugs or barrier film by incorporating diborane (B2H6) into the gas mixture to dope the TiCl4-based titanium nitride film during the deposition process. The addition of B2H6 to the precursor gas used to form the TiCl4-based titanium nitride film has been found to improve the mechanical properties of the resulting titanium nitride film with substantially no impact on its conductive properties. In particular, the gaseous mixture used to form the boron-doped, titanium nitride contacts comprises diborane (B2H6) in an amount effective to provide a contact having an amount of boron to provide a level of adhesion of the conductive contact to the insulative sidewalls of the contact opening to substantially eliminate peeling of the contact from the sidewalls and cracking of the body of the insulative layer. The mixture further includes an amount of ammonia (NH3) to provide the contact with a level of nitrogen effective to maintain the conductivity of the contact at a predetermined level for an effective electrical contact with a conductive or active area within the substrate to/from an active area within a semiconductor device and/or a memory or logic array.
In one aspect, the invention provides methods for forming a titanium nitride conductive contact in a via or other contact opening of a semiconductor structure. The opening is formed through an insulative layer to a conductive area, such as a source/drain region, in an underlying silicon substrate. The method is particularly useful for forming conductive contacts within vias and other openings having an aspect ratio of about 3:1 or greater, and a width dimension of about 0.25 xcexcm or less.
According to one embodiment of the method of the invention, a titanium nitride conductive contact is formed by first depositing a seed layer comprising titanium silicide (TiSix) over the silicon substrate at the bottom of the contact opening, preferably to a thickness of about 250 to about 300 angstroms. Preferably, the TiSix seed layer is deposited from titanium tetrachloride (TiCl4) and hydrogen (H2) by plasma-enhanced chemical vapor deposition (PECVD).
A boron-doped titanium nitride film (i.e., titanium boronitride, TiBxNy) is then deposited onto the seed layer to fill the contact opening, typically to a thickness of about 1000 to about 3000 angstroms. Preferably, the TiBxNy layer is deposited from a gas mixture of TiCl4, NH3, B2H6, and one or more carrier gases, by thermal CVD at a pressure of about 1 to about 15 Torr and a temperature of about 550 to about 700xc2x0 C. The substrate can then be processed to remove excess material, for example, by chemical-mechanical polishing, to form the conductive contact in the opening.
In another embodiment of the method of the invention, a multi-layered titanium nitride conductive contact is formed within a contact opening of a semiconductive structure. A titanium silicide seed layer is first formed over the silicon substrate at the bottom of the contact opening. To form the layered contact, alternating layers of titanium nitride and boron-doped titanium nitride are then deposited over the seed layer. In forming the alternating layers, a layer comprising titanium nitride (undoped) can be deposited from a first gaseous mixture comprising TiCl4 and NH3, to form a layer typically about 100 to about 500 angstroms thick. Diborane (B2H6) can then be introduced into the gaseous mixture to deposit an intermediate layer of boron-doped titanium nitride to form a layer typically about 100 to about 500 angstroms thick. The flow of diborane into the gas mixture can then be stopped to deposit a next layer of titanium nitride layer that is not doped to a typical thickness of about 100 to about 500 angstroms. Additional alternating layers of doped and undoped titanium nitride can be deposited to fill the opening, with the uppermost layer being undoped titanium nitride.
Another aspect of the invention is a conductive contact formed in a semiconductor structure of a semiconductor circuit. The semiconductor structure comprises a silicon substrate, an overlying insulative layer, a contact opening formed through the insulative layer to expose the underlying silicon substrate, and the conductive contact formed within the opening.
In one embodiment of the conductive contact according to the invention, the contact comprises a layer of boron-doped titanium nitride overlying a thin titanium silicide layer formed on the substrate at the bottom of the opening.
In another embodiment, the conductive contact comprises multiple layers of titanium nitride overlying a thin titanium silicide layer deposited onto the silicon substrate at the bottom of the contact opening. The contact comprises alternating, overlying layers of undoped and boron-doped titanium nitride that fill the contact opening. An undoped titanium nitride layer overlies the titanium silicide layer, and also forms the uppermost layer of the conductive contact. The thickness of each of the individual layers is typically about 100 to about 500 angstroms.
Another aspect of the invention is an integrated circuit (IC) device that includes the foregoing conductive contacts comprising boron-doped titanium nitride. The IC device comprises an array of memory or logic cells, internal circuitry, and at least one generally vertical conductive contact coupled to the cell array and internal circuitry.
In one embodiment of an integrated circuit device according to the invention, the IC device comprises a conductive contact of boron-doped titanium nitride that is formed within an insulative contact opening over a thin layer of titanium silicide deposited onto the exposed substrate at the bottom of a contact opening. In another embodiment of an integrated circuit device, the conductive contact is multi-layered and comprises alternating layers of titanium nitride (undoped) and boron-doped titanium nitride deposited onto a titanium silicide layer overlying the substrate at the bottom of a contact opening. The contact is in electrical contact with a conductive area or active area such as a source/drain region of a transistor or a memory or logic cell array, or other semiconductor device.
Advantageously, the present film overcomes limitations of tungsten plug fills in high aspect ratio devices, with parametric data showing superior results compared to that of tungsten. The present invention provides processes for forming conductive contacts that are fast, simple and inexpensive to implement in semiconductor manufacturing.